The long-range objective of this research program is to determine the mechanisms of regulation of both the levels of expression and the distribution of molecules on the surfaces of muscle fibers and neurons. These parameters are central to proper functioning of muscle and nerve. The mechanisms regulating them are an integral part of the genesis of normal, adult phenotypes of cells. Defects in these parameters are involved in numerous disorders, including myasthenia gravis and demyelinating diseases. We have used monoclonal antibodies to define individual cell-surface glycoproteins and are using these in determining the details of biosynthesis, processing, incorporation into plasma membrane, turnover, distribution on muscle fibers and neurons. Among these glycoproteins are a glycoprotein which is involved in rapid traffic from surface to lysosome and another which is the Na/K ATPase (or sodium pump). This molecule is of special importance for survival of all cells and plays a crucial role in maintaining excitability of muscle and nerve. Our goals in studying the Na/K ATPase include (1) working out the details of its biogenesis, (2) determining the mechanisms of up-regulation, (3) describing its distribution in quantitative terms on myelinated axons and in sarcolemma and T-tubule systems of muscle fibers, (4) exploring the correlation between Na/K ATPase and the intramembranes particles seen in freeze-fracture replicas, (5) exploring the molecular heterogeneity of Na/K ATPase, and (6) using Na/K ATPase as a focus for studies on the genesis of new membrane during neurite outgrowth. We are extending our studies to the nucleic acid level in order to answer, on a more basic level, questions of molecular heterogeneity of Na/K ATPase and mode of assembly during biogenesis. These studies should yield primary amino acid sequences of Na/K ATPase subunits and should prepare us for future studies of structure-function and structure-regulation relationships, which we expect to involve in vitro genetics.